Docker : Use Persistent Storage2019/07/24

	When Container is removed, data in it are also lost, so it's necessary to use external filesystem in Container as persistent storage if you need.
[1]	For exmaple, create a Container only for using to save data as a storage server with an image busybox.

root@dlp:~#

vi Dockerfile

# create new

FROM busybox
MAINTAINER ServerWorld <admin@srv.world>

VOLUME /storage
CMD /bin/sh

# build image

root@dlp:~#

docker build -t storage ./

root@dlp:~#

docker images

REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
storage                    latest              51e28000b0fb        2 seconds ago       1.22MB
web_server                 latest              42e95a62ed8e        16 minutes ago      300MB
srv.world/debian_apache2   latest              4295df3e5c82        22 minutes ago      243MB
busybox                    latest              db8ee88ad75f        5 days ago          1.22MB
debian                     latest              00bf7fdd8baf        2 weeks ago         114MB

# generate a Container with any name you like

root@dlp:~#

docker run -it --name storage_server storage

/ #

exit

[2]	To use the Container above as a Storage Server from other Containers, add an option [--volumes-from].

root@dlp:~#

docker run -it --name debian_server --volumes-from storage_server debian /bin/bash

root@da389fad6f25:/#

df -hT

Filesystem                  Type     Size  Used Avail Use% Mounted on
overlay                     overlay   63G  4.6G   55G   8% /
tmpfs                       tmpfs     64M     0   64M   0% /dev
tmpfs                       tmpfs    7.9G     0  7.9G   0% /sys/fs/cgroup
/dev/mapper/debian--vg-root ext4      63G  4.6G   55G   8% /storage
shm                         tmpfs     64M     0   64M   0% /dev/shm
tmpfs                       tmpfs    7.9G     0  7.9G   0% /proc/acpi
tmpfs                       tmpfs    7.9G     0  7.9G   0% /sys/firmware

root@da389fad6f25:/#

echo "persistent storage" >> /storage/testfile.txt

root@da389fad6f25:/#

ls -l /storage

total 4
-rw-r--r-- 1 root root 19 Jul 24 04:43 testfile.txt

[3]	Make sure datas are saved to run a Container of Storage Server like follows.

root@dlp:~#

docker start storage_server

root@dlp:~#

docker exec -it storage_server cat /storage/testfile.txt

persistent storage

[4]	For other way to save data in external filesystem, it's possible to mount a directory on Docker Host into Containers.

# create a directory

root@dlp:~#

mkdir -p /var/lib/docker/disk01

root@dlp:~#

echo "persistent storage" >> /var/lib/docker/disk01/testfile.txt

# run a Container with mounting the directory above on /mnt

root@dlp:~#

docker run -it -v /var/lib/docker/disk01:/mnt debian /bin/bash

root@8490041a0db2:/#

df -hT

Filesystem                  Type     Size  Used Avail Use% Mounted on
overlay                     overlay   63G  4.6G   55G   8% /
tmpfs                       tmpfs     64M     0   64M   0% /dev
tmpfs                       tmpfs    7.9G     0  7.9G   0% /sys/fs/cgroup
/dev/mapper/debian--vg-root ext4      63G  4.6G   55G   8% /mnt
shm                         tmpfs     64M     0   64M   0% /dev/shm
tmpfs                       tmpfs    7.9G     0  7.9G   0% /proc/acpi
tmpfs                       tmpfs    7.9G     0  7.9G   0% /sys/firmware

root@4526babc56ec:/#

cat /mnt/testfile.txt

persistent storage

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